Electrical gating circuits



Nov. 17, 1953 D. L.. cum-ls 2,659,815

ELECTRICAL GATING CIRCUITS Filed OC'b. 30, 1951 5 Sheets-Sheet l "Y @MJWZK NOV. 17, 1953 v D, CUR-ns 2,659,815

. yELECTRICAI.. GATING CIRCUITS Filed V0G13. 30 1951 5 Sheets-'Sheet 2 Nov. 17, 1953 D. L. CURTIS ELECTRICAL GATING CIRCUITS` 5 Sheets-Sheet 3 Filed Oct. 30 1951 INVENToR. fM//a 6.//47/5, BY

Nov. 17, 1953 D. l.. CURTIS 2,659,815

ELECTRICAL CATINC CIRCUITS Filed oct. 3o, 1951 5 sheets-sheet 4 Nov. 17, 1953 D. L. CURTIS 2,659,815

yELECTRICAI.. GATING CIRCUITS Filedoot. so, 1951 5 sheets-sheet 5 Patented Nov. 17, 1953 ELECTRICAL GATING CIRCUITS Daniel L. Curtis, Venice, Calif., assig'no'r toHughes rliool Company, Houston, Tex., a corporation of Delaware Application October 30, 1951, Serial.No.-253,903"

This invention relates to electrical gating cir"- cuits and more particularly to electrical gating circuits employing neon tubes.

Gating circuits have found widespread application in electronic fields and many types have been deveioped to perform various gating functions. In particular, the gating function wherein a pulse is to be passed or blocked upon the occurrence of non-occurrence of a gating signal, respectively, lhas been provided for by pentode circuits, vacuum tube diode circuits, crystal diode circuits, triode circuits, and other types of circuits. Ihe majority of these gatng circuits have proved satisfactory for the gating operations intended, butl all lack the ultimate in reliability owing to the unpredictability oi vacuum tube or crystal diode life.

This invention provides gating circuits performing the function set forth above which employ neon tubes as their primary component. One commercially available neon tube is rated at 25,000 hours of active conduction which, when considered with the fact that a neon tube in such a gating circuit will conduct only intermit tently, provides an exceptionally high degree of reliability, comparable to such circuit components as resistors and capacitors. ity appreciably decreases the maintenance and service cost of gating circuits so constructed.

Another advantage gained by utilizinggating circuits according to the present invention lies in the relatively low initial cost of such neon tubes as compared with the before-mentioned diodes, triodes, pentodes, etc. Thus, the nancial saving will be appreciable when gating circuits are utilized in a devicel such as a digital Such reliabil-` computer, where an extremely large number willi Y be required. Also, in applications involving airborne equipment, the saving in weight and size by employing neon tube gating circuits will likewise be considerable.

The gating circuits according to the present invention utilize the constant voltage characteristic of neon tubes. The gating signals are applied across the electrodes of the neon Atube through a resistor and the ensuing` conduction,

during the interval of each gating' pulse, opens the gating circuit. rlhe input pulses to the gating circuit are applied between one electrode of" cuit is open is passed by the circuit andappears between the other electrode of the tube and ground. All other input pulses are blocked' by the gating circuit, owing to the Open cirbutbe hal/10il of the neon tube when non-conducting,

the normal conducting potential. This difference of potential between the firing and conducting potentials is greatest for cold neon tubes, that is neon tubes which have not recently been conducting, and is much smaller for neon tubes which have only recently ceased conduction. In theformer case, spurious output pulses are produced whenever the neon tube lires as When,. for exam-ple, the` gating circuit opens. The neon tubegating circuits are thus unsatisfactory when the lgating signals are of infrequent occurrence.

However, in applications Where the gating signals recur rapidly, as might be the case in high speed digital computer applications, gating circuits composed of thesev neon tubes perform satisfactorily and produce no undesired or spurious output pulse upon each ring of the neon tube. Gating circuits employing ideal neon tubes whose firing and conducting potentials are very close together are satisfactory for both infrequently and frequently occurring gating signals.

'll'ie present invention also provides circuitry for use with the type of neon tube most readily commercially available which enables these tubes to operate satisfactorily in neon gating circuits having infrequently occurring gating signals. This is done, in one instance, by applying a potential to a conductive coating on the glass envelope of the neon tube, the potential being of suchl polarity and` magnitude as to speed conduction therein by producing ionization of the f neon gasmolecules separate and distinct from the ionization produced by the applied gating signal. One suitable conductive coating is Aqua-- dag, a colloidal dispersion of nely ground graphite manufactured b-y the Acheson Colloids Company of Port Huron, Michigan. In another instance, means are disclosed by the present invention to producethis additional ionization by employing a radio-frequency electromagnetic field in the vicinity of the tube, the field continuously maintaining ionization ofthe neon gas in such amount as to allow firing oi the tube at a potential just above its normal conducting potential upon application of' the gating signal. In stillanother instance, a quantity ofv radioactive material, placed yadjacent the neon tube, produces ionization of a portionV of the gas molecules whereby the applied gating signal produces conduction through thetube at a potential just above the conduction potential thereof.

i rIhis invention also discloses a combination of and and or gating circuits' employing neon tubes and constructed according to the principles of the present invention wherein gating operations rnay be had at infrequently occurring gating signals.

It is, therefore, an object of this invention to provide an electrical gating circuit composed of neon tubes for passing and blocking electrical input pulses upon the occurrence and non-occurrence of electrical gating signals, respectively.

Another object of this invention is to provide an electrical gating circuit including a neon tube and responsive to an electrical gating signal applied across the tube to fire the tube and open the gate.

Still another object oi this invention is to provide an electrical gating circuit including a serially-connected neon tube and resistor, said tube being responsive to an electrical gating signal applied across the series combination to rire and allow any input signal applied to one of its electrodes to appear as an output pulse on its other electrode.

A further object of this invention is to provide an electrical gating circuit employing a neon tube for use at infrequently occurring gating signals by producing ionization of the neon gas within the tube in addition to the ionization produced by application of a gating signal across the electrodes of the neon tube whereby the tube fires at a potential only slightly in excess oi its normal conducting potential.

A still further object of this invention is to provide a gating circuit employing a neon tube for use at infrequently occurring gating signals by producing extra ionization within the tube by application of a potential of correct magnitude and polarity to an aquadag" coating on the glass envelope of the neon tube simultaneously with the occurrence of each gating signal whereby the tube rires at a potential only slightly in excess of its normal conducting potential.

Another object of this invention is to provide a neon tube gating circuit for use at infrequently occurring gating signals by ionizing a portion of the neon gas molecules therein by applying radio-frequency energy thereto whereby the tube fires upon the gating signal attaining a potential only slightly in excess or' the normal conducting potential oi' the tube.

Another object of this invention is to provide a neon tube gatlng circuit i'or use at infrequently occurring gating signals by continuously ionizing a portion of the neon gas molecules within the neon tube by a radioactive substance whereby the tube fires whenever the gating signal reaches a potential only slightly in excess oi the normal conducting potential or' the tube.

The novel features which are believed to be characteristic ol the invention, both as to its organization and method of operation, together rwith further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which several embodiments of the invention are illustrated by way oi` example. It is to be expressly understood, however, that the drawings are i'or the purpose of illustra tion and description only, and are not intended as a definition of the limits of the invention.

Fig. l is a circuit diagram o one form of a neon gating circuit according to the present invention;

Fig. 2 is a group of potential waveforms illustrating the ring behavior of a neon tube;

Figs. 3cr-3h are a group of waveforms of the 4 signals appearing at various points in the circuit of Fig. 1;

Fig. 4 is a circuit diagram ci another embodiment of a neon gating circuit according to the present invention;

Fig. 5 is a group of potential waveforms illustrating the ring behavior of the neon tube within the gating circuit of Fig. 4;

Fig. 6 is a circuit diagram of a combination of neon gating circuits according to the present invention;

Fig. 'l is a group of waveforms or the signals appearing at various points in the circuit ci Fig. 6; and

Figs. 8a and 8b are schematic diagrams ci' a portion of the circuit of Fig. 1 disclosing other embodiments of the present invention.

Referring now to Fig. 1, there is illustrated one embodiment of a neon tube gating circuit aoco1 ing to the present invention. One output termi-inal of a device for producing alternate high and low voltage levels, such as a flip-flop it, connected to one electrode of a gaseous disons.: tube, such as neon tube Il, through a conclue tor I5 and a pair of resistors l2 and i3. A decoupling capacitor i4 is coupled between the coinmon junction of resistors I2 and it and ground. rEhe other electrode of neon tube I i is connecter?. through a resistor l5 to the positive te oi a source (not sho-wn) of direct-current pottial, the other terminal of the source being grounded. The voltage of the source for example, 105 volts. The output terminal ci' a negative pulse source, such as blocking oscillator I1, is connected through couplingr capacitor iii to the point of junction le of resistor 13 and neon tube il. A diierentiating circuit, comprising a series capacitor 2l and a shunt resistor' ft2, is connected to the junction point 2li oi resistor It and neon tube l i and includesan output terminal 23 connected between diilerentiating resistor 22 and capacitor 2|.

Neon tube li contains two electrodes and :t quantity of neon gas sealed within a glass envelope, tube il normally constituting an eleci ical open circuit across its two electrodes. However, upon application of a suiiicient potential dA ence across the two electrodes, ionization ci' the neon gas molecules occurs and, after fori' of suiiicient ions, current conduction is init between the electrodes.

Upon conduction, the potential drop across the neon tube decreases from a iiring level, that is the potential difference required to initiate conduction, to a conducting level, the conducting level remaining substantially constant for a wide variation of current ilow through the tube. For a majority of commercially available eon tubes, hereafter referred to as commercial neon tubes, the firing level is of the order of to 90 volts, while the conducting level is approximately 50 volts.

When the applied potential is removed, the current flow through the tube ceases, leaving a quantity of charged ions, the number of ions clecreasing rapidly with time. If, immediately after removal, the potential were reapplied, the tube would fire at an applied potential of over 50 volts, but considerably less than the 80 to 90 volts no1-- mally needed to fire a cold neon tube, that is, a neon tube initially having no charged ions therein. This result follows from the fact that the firing potential is no longer required to generate all of the required number of ions before ring occurs, since charged ions remain from the asse-gaie previous conduction period. `As the interval ofi time between the vend of the previous conduction period and the instant of reapplication of the ring potential increases, the number 'of remaining charged ions decreases, and the reapplied poteni tial must rise to refre the tube.

This phenomenon is graphically illustrated in 2 for the commercial neon tubes. Here, the waveform of the potential drop, generally designated 25, across a conducting neon tube isillus-V trated as the applied potential is removed. `Along the time axis, various potentials are illustrated as reapplied across the neon tube at different time intervals after termination of the originally applied potential. Thus, a potential, as indicated at 2li, is applied at a time t1 shortly after waveform reaches 0 volts. Potential 26 must rise-'to slightly more than the volts normal conducting potential of the neon tube before the tube ires. The magnitude of the diiference between the maximum applied or firing potential and the conducting potential is designated by e1' which is, in this particular example, relatively small. In the same manner, the potentials, designated and 28, are illustrated as applied across the neon tube at increasingly greater time intervals t2 and t3, respectively, and must rise to increasingly greater potentials e2 and es, respectively, above the normal conducting potential of 50 volts before ring takes place. Those neon tubes having a ring potential only slightly in excess of their conducting potential, regardless of the time interval from their previous conduction period, are hereafter referred to as ideal neon tubes.

Referring now to Fig. 3, there is illustratedra group of waveforms revealing the operational characteristics of the gating circuit according to Fig. 1. In Fig. 3a, the output signal, generally designated I0', produced by iiip-op It, comprises alternate high and low voltage levels of 105 and 0 volts, respectively. In Fig. 3b, the output signal, generally designated I1' of oscillator I'I, includes a series of pulses occurring, by way of example, substantially in the middle of the successive voltage level intervals, respectively, of signal I0', each of the pulses having-a magnitude of 50 volts. In Fig. 3c, the signal generally designated II', is the signal appearing across neon tube I I, as measured between junction points I9 and 2t, while in Fig. 3d, the signal generally designated 20 is the signal appearing between junction point 20 and ground. The output signal, generally designated 23', of the gating circuit appearing on output terminal 23, is illustrated in Fig. 3e.

When ip-iiop I0 is producing its high voltage level of 105 volts on conductor I5, as before the first low voltage level Illa of signal I0', the potential difference across neon tube II is of 0 volts magnitude since the voltage of junction 2D also is 105 volts. When nip-nop I0 produces its first low voltage level IIIc, the potential difference across neon tube II increases negatively as measured from junction point I9 to junction point 20, as illustrated by level IIa of 4signal II. The fall to level I Ia is not as rapid as the downward drop of the output voltage of flip-flop I0 since a portion of the ilip-ops energy is shunted 1 to ground through decoupling capacitor I4 and I the relatively low output impedance of blocking oscillator I'I.

If it is assumed that ions will remain from the previous conduction period, the potential difference across neon tube II continues to increase until just in excess of 50 volts, at which time tube cao I'I `fres and? signal' I I :instantaneouslyreturns lto the-50rvo1t conducting level;V asindicated at 30'.V This instantaneous return of signal II appears as-.a pulse 3|' of signal 20 Vat junction point 20,

owing lto' the constant Voltage characteristic of neon tube I I, and as slight pulse 32 of signal 23' on output terminal 23.

The period of conduction of neontube I I is indicat'ed by thefflat -portion of level' I Ia of signal II having approximately `50 volts potentiali- During this conduction period, vthe currentflow from the 105 volt positive terminal to flip-nop Ill produces, besides the 50 volt potential drop' across neon tube Il a 55 volt drop across resistors I2, I3

and I6. vThe value of resistor I is made -ap- The iirst pulse Ila of input signal I'I occurs in the middle of iirst level I Ia of signal II andl is conducted to junction It through capaoitor'l. Input pulse I'Ia, atjunction IS, has two parallel paths of travel, one through neon tube I I and resistor I6 to the 105 volt terminal and groundr and the other through resistor I3 and decoupling capacitor I4 to ground. Capacitor I4 shunts to ground the portion of the input pulse directed thereto to prevent it from triggering nip-nop I0 through lthe youtput circuit thereof. 'y The portion of pulse Ila" conducted along the other path appearspartly across neon tube II as pulse 29a of signal II', the remaining portion appearing across resistor It as a pulse'33 of signal 20'. Pulse 29a results from the fact thatl neon tube I I is not a perfect constant potential device, especially with respect to signals of rapid rise time, and presents a finite value of impedance thereto'. However, by carefully selecting the circuit parameters, pulse 29a may be made approximz` tely onefourth of the magnitude of pulse 33. Pulse d3'v is differentiated by differentiating capacitor 2I and resistor 22 and appears as a pulse 34' of output signalZZi on output lterminal 23.

When iiip-ilop It produces its next high Voltage level IBD', the potential difference across neon'l tube II returnsto 0 voltwith a corresponding cessrtion of conduction as is illustrated by level IIb' of signal II'. The next negative pulse I'Ib' from oscillator I'I, occurring during this 0 voltage level, yis blocked by the neon gating circuit since neon tube I I is an open circuit device in its nonconducting state. Accordingly, all of pulse I 'Ib' appears across the electrodes oi the tube as is illustrated by the pulse 29h of signal II'. .Although the potential of the pulses7 as illustrated, is only 50 volts negative, the pulses would not, even if of a much greater magnitude, i. e., volts negative, re neon tube II owing to their extremely short duration. The required ilring potential must be applied across a neon tube for a definite interval of time before the gas therein is ionized sufficiently for the tube to fire. The gating signal, that is the signal which closes the gating circuit by producing conduction through neon tube II, may be considered to be the low voltage level of flip-flop lil taken in conjunction with the volt source of positive potential whereby the totrl potential diiference across neon tube I I exceeds the firing potential thereof.

The gating circuit of Fig. 1, when employing ideal neon tubes, that is,'those neon tubes Whose firing and conducting potentials -are relatively ,close'togethn voperates satisfactorily Afor gating t autumn at, it

eiesogsw to the termination of its corresponding gating signal. In general, the maximum gating frequency of 50 kilocycles may be employed when the input pulses to be passed occur substantially simultaneously with the termination of their respective gating signals.

Stated differently, each new gating signal must be applied from flip-flop Ill across neon tube II within at least 330 microseconds but not less than,

under the above referred to most favorable conditions, microseconds after the termination of the preceding gating signal. At gating frequencies less than 3 kilocycles, the operation is unsatisfactory owing to the production of spurious output signals while the operation is unsatisfactory at gating frequencies higher than 50 kilocycles owing to the slow response speed of the tube.

Figs. 3c through 3e reveal signals illustrating the satisfactory operation of the neon gating circuit of Fig. 1 employing a commercial neon tube when the frequency of gating signal I0 lies between 3 and 25 kilocycles, the upper frequency limit being due to the application of each pulse from oscillator I I during the middle of each gating signal level. These signals also illustrate the operation oi a neon gating circuit at any frequency of gating signals under kilocycles when the circuit employs an ideal neon tube, that is one having similar iii-ing and conducting potentials.

Figs. 3f through 3h illustrate an unsatisfactory operation of a neon gating circuit employing a commercial neon tube with a gating frequency less than 3 kilocycles. The signal appearing across neon tube II, generally designated I", is of the same general shape as was signal II previously described in connection with the higher gating signal frequency. However, owing to the much lower gating signal frequency in this example, the potential of the signal across tube II must rise to a higher value before iiring occurs. Accordingly, the potential drop 3D" of signal I I is of considerably greater magnitude than drop of signal Il', and, in turn, produces a much larger negative pulse 3I" of signal 25J". Pulse 3I corresponds to pulse 3l of signal 20 of the previous case, and appears as a spurious pulse 32 in output signal 23". An input pulse Ila, occurring during level Ila", is passed by the gate and appears as a desired output pulse 34" of output signal 23". Spurious pulse 32 and output pulse 34 are of the same order of magnitude owing to the large initial magnitude of the potential drop 30" and are indistinguishable for practiea1 purposes, thereby making the output signal of the gating circuit of Fig. 1 inaccurate.

If blocking oscillator I'I produced positive insteed of negative pulses, the gating circuit would be inoperative since each positive pulse, occurring during the time interval neon tube I i is conducting, would extinguish conduction in the tube by raising the potential of junction point I9 toward the potential of junction point 2D. If it is desired to utilize this gating circuit with positive input pulses, oscillator I1 and coupling capacitor I8 Should be coupled to junction point 20, while aquadag E. the 'output differentiating circuit should be coupled to junction point IS. The positive pulses produced when neon tube II was conducting would occur primarily across resistor I8 owing to the constant voltage property of the neon tube.

Referring now to Big. 4, there is illustrated another ernbodiment oi a neon gating circuit according to this invention whereby a commercial neon tube may be satisfactorily employed in a gating circuit for a gating signal frequency range of 0 up to at least 25 kilocycles. The neon gating circuit of this embodiment includes the same structure as the gating circuit according to Fig. 1, the like elements of the two devices herein being given the same numerical designation as before b-ut preceded by the prex 4. The gating circuit according to l has, in addition to the structure illustrated in Fig. l, conductive material, such as an auuadag coating 3E on the glass envelope ci' neon tube il i. The aquadag coating in this example is a deposit ci finely divided graphite particles on outer glass surface of the tube envelope. The other output terminal of bistable flip-liep diri, which produces a signal complementary to signal iii of Fig. 2 and is not illustrated in Fig. 1, is connected through a conductor and a resistor 35 to aquadag coating The lead capacitance to ground of the connection from conductor 38 to coating 35 is illustrated by a capacitance Sai, herein shown dette.

Reference to the curves illustrated in Fig. 5 taken in conjunction with the signals of Figs. 3a

irough Bc best illustrate how satisfactory operation of a commercial neon tube in a gating circuit at gating ireruiencies below 3 kilocycles as well as at the higher frequencies, is accompli-shed. In particular, assume gating signal is decreasing from its high voltage level oi' 105 volts to the low voltage level 10a oi 0 volts, as illustrated in Fig. 23a. This fall of potential on output conductor liti corresponds to an equivalent rise of the potential applied from the other output conductor of nip-flop Ill to coating 23135 and the voltage on aquadag coating Eli, generally designated 36 in Fig. accordingly rises iroin a O value to i volts positive.

immediately preceding level itu oi signal ID', the inner surface of the glass envelope of neon tube fill was 105 volts positive with respect to ground owing to the 105 volt potential applied to both of the electrodes ther of. 'Upon the rise of potential 3G on aquacL coating- 36, as produced by the subsequent triggering of flipiiop die, the inner suriace of the glass envelope of neon tube ilI is correspondingly elevated above 105 volts through condenser action between the surface the aquadag coating 36. This potential rise above volts of the inner glass surface oi' the neon tube, generally designated t9 in Fig. 5, occurs siinuitanecusly with the decrease of the potential. applied from conductor M5 to one electrode oi neon tube .fill is indicated at til in lfig. 5. The potential diierence of potentials Eil and Mia produces ionization of the neon gas independent of the ionisation produced by the potential difference existing across the neon tube electrodes. This additional ionization is effective, ii produced at the correct time, to allow the firing of neon tube liII to taire place much sooner Jrhan would have been possible had the only ionization produced been through the potential difference existing across its electrodes. Accordingly, the potential appearingz-acrossfneon tube y4I Ligenerally designated 4Ilaf in Fig. 5.,.rises only slightly above 50 volts, at. which time t1, conduction occursowing to the additional ionization afforded the neongas by potential 33. Neon tube 4I I then assumes its normally conducting potential of 5G volts.

For comparison purposes, the potential across neon tube lil without aquadag.coating 33 for low frequency gating signals isl illustrated at di ib in Fig. 5 and is similar to that illustrated i'or the low frequency operation of the gating circuit oi Fig. 1 employing a commercial neon tube as shown in Figs. {if-3h. Thus, potential filib must riseto approximately 80 volts at a time t2 before. neontube 4II conducts and is similar to level Ila of signal iI" of Fig. 3]'. It is thus seen that,aquadag coating 35, when maintained at ythe ,potential of the other iipiiop output conductor 334;v allows gating operations to be performed at extremely low gating frequencies without production of spurious output pulses.

The value of resistor 35 ci Fig. 4 isoletermined-by the rise time of the potential across neon tube ill when nip-flop Md triggers into its low voltage level on conductor'l. As has been stated previously, this applied potential does not rise as fast as the potential output of flip-nop file owing to the shunting effect of both decoupling capacitor 4 I il .and the 'low output impedance of oscillatorlll. It is, therefore, necessary that the potential applied tothe aquadag coating 36 from output terminal 38 of 4flip-flop till be delayed approximately the same amount. Ii no such delay were introduced, thepotential of signal 3d would rise in a substantially instantaneous manner to its maXi-mumivalue throughthe beforementioned condenser action and then return t 105 volts. rIhe ions thus produced would have time to deionize before timevv t1 were reached with, the result that the operation oi the gating circuit of Fig. 4 at low frequency gating signals would be similar to thatV described for the gating circuit oi Fig. 1 in Figs. 3f3h.

To alleviate this difculty, a resistor 35 is incorporated in the conducting path between output conductor 38 of nip-nop 413 and aquadag coating to delay therise time of the potential Zit' of Fig. 5. in value to the leadtoground capacitance 3'! that the peak of the additional ionization produced by signal 3@ is reached concurrently with the attainment or 5) volts by signal 4I I. With this condition fulfilled, neonA tube fiII will begin conducting at an applied Apotential only' slightly higher than the conducting potential as at lli la' of Fig. 5.

"'Tig. 6 discloses one combination of .and and or gating circuits employing the principlesv of the present invention as might .be suitable for use in digital computer operations. It is to be understood that` the particular'y combination shown is not exhaustive of possible combinations but is intended only as illustrativeoi Ythe principles involved.

1n particular, there is illustrated in Fig. 5,'two and gate circuits 49 and all,V the outputs of which are applied to theinputs of an.or" gate circuit 42. The output of or gate circuit 42 is, in turn, applied as gating signals to a neon gatingcircuit 13 of the typev illustrated in. Fig. 4. And gate circuit IllV comprises. abus 41 ccnnectedK tothe positive terminal ofaSOfl voltsource of potential. (not shown) through. a Vresistor 43.

Resistor 35 should be so related f 10 Afneon tubev is connected between bus 41 and one output terminal of a nip-flop 5 I, while a neon tube 52 is connected between bus 41 and one outputterminal of a flip-nop 53.

And ygate circuit 4I, similar to circuit 40, includes a bus 55 connected to the positive terminal of the 300 Volt source through a resistor 56. A neon tube 58 is connected between bus 55 and one output terminal of a flip-flop 59, and a neon tube 5I] is connected between bus 55 and the output terminal of flip-flop 53 which was connected to neon tube 52.

Or gate circuit 42 comprises a neon tube 65 connected between a bus 64 and bus 41 of circuit 40, and another neon tube 66 connected between bus 64 and bus -55 of circuit 4I. Bus 64 of circuit 42 is connected to a positive terminal of a 20 volt source of potential (not shown) through a resistor 61.

The neon gating circuit 43 comprises a neon tube 69, one electrode of which is connected through a resistor 10 to bus 64, and the other electrode of which is connected to ground through a resistor 1I. Blocking oscillator SI1 and coupling capacitor BI8, corresponding to oscillator I1 and capacitor I8 of Fig. 1, are coupled to the junction of neon tube 59 and resistor 1I. Diierentiating capacitor 62! and resistor 622, corresponding to capacitor 2| and resistor 22 of Fig. 1, are included in gating circuit 43, capacitor 62I being connected to the junction of resistor 10 and neon tube 53. Output terminal 523, corresponding to terminal 23 of Fig. 1, is connected to the junction of differentiating resistor 622 andcapacitcr 62|.

The combination, as described, would operate satisfactorily if ideal neon tubes are used. However, if commercial neon tubes are to be employed, it is necessary to incorporate additional structure similar to that employed in the gating circuit of Fig. 4. Accordingly, each neon tube has an aquadag coating, each coating being supplied with a potential of correct magnitude and polarity as is necessary for low speed operation of the device. These potentials are produced by a flip-flop 13, one input terminal of which is connected directly to the output terminal of blocking oscillator SI1, the other input terminal being connected through a delay means, such as delay line 12, to the output terminal of oscillator SI1. One output conductor 14 of flip-flop 13 is connected to the aouadag coating` on neon tubes 50, 52. 58 and 50 through resistors 15, 1E, 11 and 18, respectively, while the other output conductor 19 of flip-flop 13 is connected to the aquadag coatings on neon tubes 55, 63 and 69 through resistors 8l), 8l and 82, respectively.

The operation of the device according to Fig. 6 may be best explained by reference to the waveforms illustratedin Fig. 7. Each of the output signals of flip-flops 5I and 53, generally designated 5 I and 53', respectively, in Fig. 7, contains low and high voltage levels of zero and volts, respectively. By way of example, signal 5I contains a rst high voltage level 5ta of 90 volts followed by a second low voltage level 5|b of 0 volts followed, inturn, by a high voltage level 5Ic. Signal 53' contains a first low voltage level 53a followed by two contiguous high voltage levels 53h and 53o. During the interval that flip-nop 53 is producing level53a, neon tube 52 conducts and current iiows from the 300 Vvolt source throughiresistor 43, bus 41, and neon tube 52 to thev output. terminal of` fiip-iiop 53.. The signal on bus.v 41,- generally'dcsignated 41 in Fig. '7v is during this interval, at 50 volts positive, as indicated by the first level 41a, owing to the 50 volt potential drop across neon tube 52.

During the next interval, signal I falls to level 5Ib of zero potential whereas signal 53' rises to the high potential level 53h. The 50 volt potential on bus 41 remains unchanged during this period, as is indicated by level 41b of signal 41', since conduction now takes place from the 300 volt source to flip-ilop 5| through resistor 48 and the -other neon tube 50.

During the next interval, the potential of signal 53 remains unchanged as indicated by level 53o whereas signal 5| returns to high voltage level 5Ic. When flip-flops 5| and 53 are simultaneously producing their high voltage level, current will flow thereto from bus 41 and neon tubes 50 and 52, respectively. The potential of bus 41 will thereby be elevated to a 140 volt potential, as indicated by level 41c of signal 41', owing to the 50 volt drop across neon tubes 5I) and 52 and the 90 volt output potential produced by flip-flops 5I and 53.

Whenever the potential of bus 41 is 50 volts, as for example, levels 41a or 41b of signal 41', neon tube E5 is non-conductingl since bus 64 is at 20 volts positive, owing to the volt source, and only a volt potential drop exists across the tube. However, when the potential on bus 41 rises to the high voltage level of 140 volts, as shown by level 41e, neon tube B5 conducts and the potential of bus 64, generally designated 64 in Fig. 7, is elevated from 20 volts, as indicated by level 64b, to 90 volts as indicated by level 64o, the 90 volts being the difference between the 140 volt potential on bus 41 and the volt potential drop across neon tube E5. The 90 volt potential on bus 64, in turn, produces conduction through neon tube 69 and series resistors 10 and 1I thereby opening gating circuit 43. Gating circuit 43 operates similarly to the gating circuit of Fig. 4 in that all pulses produced by oscillator SI1 during the period neon tube G9 is conducting appear on output terminal 623. The output signal of blocking oscillator SI1, generally designated SI1 in Fig. 7, comprises, by way of example, a series of pulses occurring at regular intervals intermediate the voltage levels produced by flip-flops 5 I, 53, and 5B. Thus, pulse 6I1c, produced by oscillator SI1 during level 41e, is passed by gating circuit 43 and appears as a pulse 623e of the output signal on terminal 623, generally designated 623 in Fie. 7.

By wav of summary then. when flip-flops 5i and 53 simultaneously produce their high voltage level, current ilows between the 200 volt source and ground through neon tube 55 of circuit 42 and neon tube |59 thereby opening gating circuit 43. Thus, any negative pulses produced by oscillator GII during this interval are passed by gate 43 and appear on output terminal G23. During the interval that either or both flip-flops 5| and 53 are producing their low voltage level, neon tube 55 does not conduct and electrically isolates circuit 4I) from the remaining circuitry.

It will be herein noted that the essential difference between gating circuit 43 of Fig. 6, and the gating circuit of Fig. l, is that resistor 1I, corresponding to resistor I6 of Fig. 1, is connected to ground instead of a source of positive potential. Accordingly, neon tube 69 conducts when the potential of the signal on bus 64 rises to its high, rather than its low voltage level as was the case in Fig. 1, Thus, for satisfactory operation, it is necessary to apply the negative pulses from oscillator SI1 to the junction point between neon tube 69 and resistor 1I, corresponding to junction point 2i) of Fig. 1, rather than the junction point between resistor "lil and neon tube 69, corresponding to junction point I9 of Fig. 1. rThis is done so that the negative pulses, when applied to the gating circuit, will accentuate rather than extinguish conduction in neon tube 69 when it is conducting. Positive pulses may be utilized in the gating circuit lit ii the connections of osvillator SI1 and the output diierentiating circuit to the tube electrode are reversed in the manner explained for the gating circuit oi Fig. l.

The operation of circuit 4I is similar to the operation of circuit as may be seen by reference to the signal on ous 55, generally designated 55 in Fig. 7, and the output signals of flip-flops 5S and 53, generally designated 59 and 53', respectively, in Fig. 7. As was the case for circuit 40, whenever flip-ops 53 and 59 simultaneously produce their high voltage level, as is illustrated by levels f and 53j, of signals 5S and 53', respectively, signal is at the high voltage level 55f of 140 volts. During the interval of level 55f, current flows from the 300 volt source through resistor 55, bus 55, neon tube 5t, bus B4, resistor 1D, neon tube 69 and resistor 1I to ground. Accordingly, pulse Gili, produced by oscillator til during level 55j, appears on output terminal S23 as pulse il23f of signal F323.

The function of or gate circuit 42 is to produce conduction through neon tube S9 to open gate circuit 43 whenever the potential on either bus 41 or 55 of and gate circuits 4D and 4|, respectively, is high. Also, or gate circuit 42 electrically isolates the two and gate circuits 46 and 4I from each other, since either neon tube E5 or 6'6, while nonconducting, is an open circuit device.

As has been stated previously, the aquadag coatings and potentials applied thereto are for use with commercial neon tubes in order that the gating circuit combination of Fig. 6 might operate satisfactorily at low gating frequencies. Thus, signal 6I1 is applied to one input terminal of flip-dop 'la and each pulse thereof triggers the flip-flop so that its high voltage level appears on output conductor 19 and its lov.7 voltage level appears on conductor 14. Each triggering pulse is also delayed one-half of e. timing interval, that is onehalf of the period of signal Ell', by delay line 12 and the delayed pulses, generally designated iii in Fig. 7, are applied to the other flip-flop input terminal. Each delayed pulse of signal'iE triggers flip-flop 13 so that its high voltage level appears on output conductor 19 and its low voltage level appears on output conductor 14. Thus, each pulse in signal 6I1' initially triggers flip-flop I3 into one state and then, after being delayed for one-half of a timing interval, triggers i'lip-ilop 13 into its other state. Therefore, the signals appearing on conductors 14 and 19, generally designated 14 and 19', respectively in Fig. 7, comprise two complementary square waves each having the frequency of the pulse repetition rate of signal SI1.

The purpose served by the aquadag coatings on the commercial neon tubes within and gate circuits 4] and 4I and the potentials applied thereto, is to prevent the opening of gate 43 when, in either and gate circuit 4D or 4|, the output signal from one nip-flop changes from its high to its `low voltage level simultaneously when the output signal from the other ilip-ilop lchanges fromV itslow to high'voltagelevel rather f than preventing spuriousoutput pulsesfon output terminal S23. For example, When 'ip-flopil is `producing high voltage leve1-5|a of Asignal 5| and flip-flop 53 is` producing low voltage level 53a of signal 53', neon tube '52 is conductingfand neon tube t is nonconducting. Upon the change of signals 5i" and' 53"' into thelowand' highy voltage-levels Sib and 5319, respectively, neonfitube 5B begins conduction vand neon tube"5./ stops 'conduction. Neon tube 5u must fire 'before flip-ilop 52 ceases conduction, otherwise the ypotential on bus 41 will rise to 30G volts'for the time interval that both neon tubes are nonconductng. As

is apparent, a potential lof 300 volts-"on bus'41 Would open gate with the "result th'atfanysignais produced byoscillator 5 i li duringthat time *interval would be passed to `output terminal 623.

This undesired operation is prevented by applying signal 'llirom flip-nop 13 to the aqu'adag coatings on neon tubes 5i) and 521 through resistors "l5 and-1%, respectively, of 'appropriate value, to allow a rapid firing ofneon tube 5i! in'this example.

As will be observed, signal lli' falls to itsiloW `voltage level each time either signal 5l .or 53 changes from one voltage leyel to the other, the reason being that dip-flop i3 is triggered at `least twice for each triggering of either flip-flop 5I or 5t. "Thus, during the interval thatthe Apotential of signal 5l' is decreasing' to level Bib,

the potential 'of signal le" applied tothe aquadag coating increasing which 'fires neon tube 5i! at just slightly above 5t volts in a manner similar to that' described for the gating circuit according to Fig. i. Neon tube 5t' will thus fire simultaneously with the conclusion' of conduction of neon tube 52 thereby preventing the'undesired opening of gating circuit 43 referred to above.

Signal 'is' is applied to the aquadag coatings oncomrnercial neon tubesii and: 5t in or gate circuit i2 to accelerate the speedl'of response thereof upon elevation of the potential on either bus'll'l orbus 55. During the interval"thatV the potential on bus l is rising to 140 volts, `as'for example, level die of signal lil', signal 7.9i appliedto the aquadag coating on neon-tube t5 isfalling to its low voltage level. As Was'the case described for the gating circuit of Fig. 4, the potential change app-lied to the aquadag coating is opposite to the potential change Within the tube, thereby producingv a rapid' evolution 'of ions by reason of the increase of 'potential difference between thextwo. The rapid production of ions, in turn, accelerates the tube conduction so thatonly a minimum time delay is "introduced by or gate circuit 42. in opening gating circuit 43.

The aduadag coating on a. commercial neon tube 65 and the application of signalg'ls.' thereto serves the identical function for gate circuit 43as did the aquadagmcoatingandsignal-applied thereto for the gating circuit "of Fig.l 4

vin thatv no spurious output* signal is produced on output terminal 523 Whenever neon tube 69 lires. Thus, whenever signall rises toits high voltage level, signal 'ifi' isifalling toits-low volt'- age level and the resulting potential' difference between the aquadag coating on neon tube and the neon gas therein accelerates the tubes iiring.

As is apparent, if ideal neon tubes were employed in the gating circuitcombination'of Fig. 6.,.the. rapid firing of such tubes'woul'dl alleviate thefnecessity forr the: aquadag coatings andfpotentials applied thereto. as* isv herein illustrated. As is alsoxapparentto. those skilled in the lart, many possible combinations exist of and and or gateA circuits comprising the neon gating circuits oi this invention, the operation and design roi-'Which are obvious from the example illus.- .trated in Fig.. 6.

Referringnow to Fig; 8c, there ishere illustrated another embodiment oi this invention wherein'suitablev operation of commercial. neon tubesmayy be. in neon. gatingl circuitsfor low ,frequency gating; signals. vQnly a portion of the neon-gating circuitof'lig. l, is again illustrated, this portion comprising. neonv tube .Il between ,junction-.points It and 2t, and; including, in addi- .re owing to the ionization produced therein by the radio-frequency energy, at an applied potential of just slightly over 50 volts. Consequently, spurious output pulses characteristic of the gating circuit of Fig. l will not be produced by the ring of neon tube l l by low frequency gating signals.

The radio-frequency energy intercepted by neon tube il in this embodiment must be carefully adiusted. Iiy the amount intercepted is too small, spuriousy output pulses will still be produced by the applied gating signals owing to a laclr. of suiiicient ionization. lf the amountintercepted` is too great, then input gating pulses from source il Willbe passed through the tube due to the large. number of ions therein regardless or" Whether a gating signal is present or not. This adjustment may be made by either varying `the positionv of coil 83` relative to neon tube I l .or byvaryng the magnitude of the output signal from. oscillator .82.

. In Fig. 8bthere isillustrated another'embodinient of this inventionsimilar to that illustrated in Fig. 8c. Here also, only a portion of the gating circuity of Fig. l, including neon tube Il between junction points la and 253 is shown, the circuit havingin addition, a quantity of radioactive substance. 8A! adjacent tube Il. Substance Bliservesthe same. purpose as does the radiofrequency energy applied to neon tube i l in the gating circuit of Figfec, that is the bombardment of. the neon 'gas molecules by the'radioactivev substance lilil produces a continuous ionization thereof.V This ionization, in turn, permits tube l I to conduct at just above a 50 volt potential difference. between junction points I9 and v2b vupon;application oi` a 'gating signal.

.The'quantity of ionization produced by substanceztllmust'be within certain limits in order -to provide proper operation of the circuit. This may be. donel by choosing the proper type and amount of radioactive substance and adjusting its position relative to neon tube l i to the proper distance. Also, substance 84'may be placed within the'glass lenvelope of neon tube l l preferably during the Vmanufacture thereof, ii" so desired, to secure thel proper. continuous ionization.

As will be apparent to these skilled in the art, either of the embodiments illustrated in Figs;Y 8a or 8b`v may be substituted for the aquadagvf coatings y and potentialsl applied thereto in the gating circuit combination of Fig. 6 when commercial neon tubes are employed therein.

as will be apparent to those skilled in the art, other types of gaseous discharge devices capable of passing current at a reasonably constant voltage drop, such as voltage regulator tubes, may be employed in the gating circuit of this invention, in addition to the commercial and ideal tubes herein specifically illustrated.

What is claimed as new is:

l. An electrical gating circuit for passing electrical input pulses upon occurrence of an electrical gating signal ci at least a predetermined voltage, said circuit comprising: a neon tube having first and second electrodes and responsive to a signal of said predetermined voltage applied across d electrodes for conducting current at a substantially constant voltage drop, said constant voltage drop being less than said predetermined voltage an electrical resistance element conductively coupled to said first electrode; means for the gating signal across the combination of said neon tube and said resistance clement; means for applying the input pulses to one of said electrodes, the input pulses applied during the occurrence of a gating signal being passed by said neon tube and appearing as output pulses on the other of said electrodes; and an output circuit ccnductively coupled to said other electrode for passing the pulses appearing thereon and blocking the gating signal.

2. An electrical gating circuit for passing electrical input pulses upon occurrence of an electrical gati g signal of at least a predetermined voltage, said circuit comprising: a g.,seous disn charge device having first and second electrodes and responsive to a signal of said predetermined voltage applied across said electrodes for con ducting current at a substantially constant voltage drop, said constant voltage drop being less tha said predetermined voltage; an electrical resistance element conductively coupled to said iirst electrode; means for applying the gating signal across the combination of said gaseous discharge device and said resistance clement; means i`or applying the input pulses to one of said electrodes, the input pulses applied during the occurrence of a gating signal being passed by said gaseous discharge device and appearing as output pulses on the other of said electrodes; and means for lowering the voltage oi the signal said gaseous discharge device is responsive to for conducting current whereby the voltage difference between said constant voltage drop and the lowered response voltage is substantially reduced.

3. The gating circuit defined in claim 2, wherein the last-named means includes a radioactive substance positioned adjacent said gaseous discharge device.

4, The gating circuit defined in claim 2J wherein the last-named means includes conducting means surrounding a portion oi said gaseous discharge device, means for producing a signal synchronously related to the gating signal, said synchronouslyuielated signal changing in potential upon each occurrence of the gating signal in a polarity opposite to that applied by the gating signal to the gas in said gaseous discharge device, and ineens for applying said synchronouslyrelated signal to Said conductive means.

5. The gating circuit defined in claim 4, wherein said gaseous discharge device is a neon tube.

5. An electrical gating circuit comprising: a gaseous discharge device having first and second 4electrodes and normally responsive to a signal of a. predetermined voltage applied across said electrodes for conducting current at a constant voltage drop, said constant voltage drop being less than said predetermined voltage; a signal source for producing alternate high and low voltage signals; means conductively coupling said signal source to said iirst electrode; a source of positive voltage, the voltage difference between the positive voltage and the low voltage signal being greater than said predetermined voltage, and the voltage diilerence between the positive voltage and the high voltage signal being less than said predetermined voltage; an electrical resistive element conductively coupled between the positive voltage source and said second electrode; said gaseous discharge device conducting current whenever the signal source produces said low voltage signal; a pulse source; means for producing alternate low and high voltage signals synchronously with the high and low voltage signals, respectively, produced by said signal source; conductive means surrounding a portion of said gaseous discharge device; means for applying the alternate low and high voltage signals to said conductive means whereby said predetermined voltage is lowered and the voltage difference between said constant voltage drop and said predetermined voltage is substantially reduced; and means for applying the pulses from said pulse source to one of said electrodes, the pulses occurring during current conduction of said gase ous discharge device appearing on the other electrode oi said gaseous discharge device as output pulses.

7. The device deined in claim e, including in addition an electrical output circuit coupled oetween the other electrode and ground.

i3. An electrical gating circuit for passing electrical input pulses upon occurrence ot an electrical gating signal of a predetermined voltage, said circuit comprising: a gaseous discharge device having rst and second electrodes and being rendered conductive by a iii-ing signal voltage applied across said electrodes, said firing signal voltage normally being greater than said predetel-mined voltage; first means for applying the gating signal across said gaseous discharge de vice; second means coupled to said gaseous discharge device for lowering the nring signal volt age at least to said predetermined voltage; and means for applying the input pulses to one or said electrodes, the input pulses applied during conduction of said gaseous discharge device bcing passed by said gaseous discharge device and appearing as output pulses on the other of said electrodes.

9. The gating circuit defined in claim 8 wherein said second means includes radiating means for enveloping said gaseous discharge device with radio-frequency energy.

10. The gating circuit donned in claim 8 where- 1n said second means includes a radioactive substance positioned adjacent said gaseous discharge device.

11. The gating circuit defined in claim s where- 1n said second means includes a conductive coat ing surrounding at least a portion of said ous discharge device and means responsive to the gating signal for applying a voltage to said coat me.

12. ln electrical gating circuit for passing electrical input pulses upon occurrence oi an electrical gating signal of at least predetermined voltage, said circuit comprising: a gaseous discharge device having rst and second electrodes and being normally rendered conductive by a firing signal voltage greater than said predetermined voltage applied across said electrodes; first means for applying the gating signal across said gaseous discharge device; second means responsive to the gating signal for lowering the firing signal voltage at least to said predetermined voltage; and means for applying the input pulses to one of said electrodes, the input pulses applied during conduction of said gaseous discharge device appearing as output pulses on the other of said electrodes.

13. The gating circuit defined in claim 1 wherein said output circuit comprises a differentiating network.

14. The gating circuit defined in claim 2 wherein the last-named means includes a source of radio-frequency energy, and radiating means conductively coupled to said energy source for enveloping said gaseous discharge device with said radio-frequency.

15. An electrical gating circuit comprising: a source of electrical gating signals, each of said gating signals being of at least a predetermined voltage; a gaseous discharge device having first and second electrodes and responsive to a signal of said predetermined voltage applied across said electrodes for passing current at a substantially constant voltage drop; an electrica1 resistive element having first and second ends; means conductively coupling said rst end to said first electrode; means for applying the gating signals from the gating signal source between said second end of said element and said second electrode; a pulse source; and means for applying the pulses from said pulse source to one of the electrodes, the pulses produced by said pulse source during the time intervals said gaseous discharge device is conducting appearing on the other electrode of said gaseous discharge device as output pulses.

16. The device of claim 6 wherein said gaseous discharge device comprises a neon tube and said conductive means comprises a conductive coating on said neon tube.

17. In combination: first and second sources of alternate high and low voltage level signals; a first source of positive potential; an and gate including iirst and second gaseous discharge devices, each of said devices having first and second electrodes, means conductively coupling the first and second sources of voltage level signals to the first electrodes of said first and second gaseous discharge devices, respectively, and

means conductively coupling the second electrode of each of said first and second gaseous discharge devices to the first potential source, said second electrodes being maintained at a first voltage when said first and second sources simultaneously produce the high voltage levels; a third gaseous discharge device having first and second electrodes; a second source of potential; an electrical resistive element conductively coupling the second electrode of said third gaseous discharge device to said second source of potential; means conductively coupling the first electrode of said third discharge device to the second electrodes of said first and second gaseous discharge device, said third gaseous discharge device 'being responsive to said first voltage for conducting current between the electrodes thereof, the second electrode being maintained at a second voltage during the conduction thereof, said second voltage being greater than the potential magnitude of said second source; a gating circuit comprising a fourth gaseous discharge device having first and second electrodes, and an electrical resistive element coupled between the second electrode of said fourth gaseous discharge device and ground; means coupling the second electrode of said third gaseous discharge device to the iirst electrode of said fourth gaseous discharge device, said fourth gaseous discharge device being responsive to said second voltage for conducting current between the electrodes thereof; a pulse source; means for applying the pulses of said pulse source to one of the electrodes of said fourth gaseous discharge device; and an output circuit coupled to the other electrode of said fourth gaseous discharge device, the pulses produced by said pulse source during the time interval said fourth gaseous discharge device is conducting appearing across said electrica1 resistive element.

18. The combination according to claim 7 wherein each of said first, second, third and fourth gaseous discharge devices comprises a neon tube.

DANIEL L. CURTIS.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,103,439 Swart Dec. 28, 1937 2,502,443 Dunn et al Apr. 4, 1950 2,539,594 Rines et al. Jan. 30, 1951 2,572,891 Smith Oct. 30, 1951 

